Investments (Valuation Allowance Rollforward by Portfolio Segment) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Mortgage Loans on Real Estate [Line Items]
Balance, beginning of period	$ 305	$ 322
Provision (release)	29	(3)
Charge-offs, net of recoveries	(9)	(25)
Balance, end of period	325	294
Commercial
Mortgage Loans on Real Estate [Line Items]
Balance, beginning of period	224	258
Provision (release)	4	(4)
Charge-offs, net of recoveries	0	(24)
Balance, end of period	228	230
Agricultural
Mortgage Loans on Real Estate [Line Items]
Balance, beginning of period	39	44
Provision (release)	2	(2)
Charge-offs, net of recoveries	0	0
Balance, end of period	41	42
Residential
Mortgage Loans on Real Estate [Line Items]
Balance, beginning of period	42	20
Provision (release)	23	3
Charge-offs, net of recoveries	(9)	(1)
Balance, end of period	$ 56	$ 22